Prose
s. B. U. III. 9
In plain words
This entry is not a piece of Śaṅkara's commentary. It is a citation marker from the printed page — a reference locator ('S. B. U. III. 9') carried over from the source, not Sanskrit content to be translated.
Close to the Sanskrit
This is not a sentence of Sanskrit text to translate. It is a page/section citation marker printed in the source (reading, expanded, something like 'Śāṅkara-Bhāṣya-Upaniṣad, [chapter] III, [section] 9') — a running reference-locator, not part of the bhāṣya's prose.